As a method of thermally igniting (self-igniting) a gaseous mixture of hydrocarbon and air, various methods are proposed. For example, for an internal combustion engine, ignition methods such as, for example, a premixed charge compression ignition method and an HCCI (Homogeneous Charge Compression Ignition) method are proposed. Starting premix type combustion as a result of pilot injection or the like in a common rail system of diesel engine belongs to such ignition methods.
For example, as for the internal combustion engine, such ignition methods have drawn attention since those ignition methods can achieve higher heat efficiency than the ignition method with spark ignition, and reduce the emission level of nitrogen oxides (NOx). However, those ignition methods have a drawback in that it is difficult to control the timing of thermal ignition.
Conventionally, ignition control devices have been proposed that control timing of thermal ignition of a gaseous mixture in a combustion region. For example, patent document 1 describes an ignition timing control device of a premixed charge compression ignition engine as an ignition control device of this kind. This ignition timing control device generates oxygen radicals by radiating laser beam oscillated by a laser generation device and collected by collecting lens toward the combustion chamber. In the combustion chamber, the oxygen radical is reacted with water vapor to form OH radical (hydroxyl radical), and the OH radical is reacted with hydrocarbon to form alkyl radical. Owing to this ignition timing control device, low-temperature oxidation reaction can be accelerated, and timing of self-ignition can be controlled.